The invention relates generally to the field of communication electronics and, more particularly, to low power consumption multiplexers.
In a communications system, a multiplexer is used to select a single output from a variety of inputs. As the number of inputs to the multiplexer increases, the complexity and power consumption of the multiplexer increases accordingly. In modern communications systems, it is commonplace to make use of multiplexers which incorporate many inputs (for example, 128) with a single output (128:1). As communication systems continue to increase in capacity and bandwidth, it is likely that these systems will require multiplexers with larger and larger numbers of inputs.
When a typical multiplexer is in use, each of the signal input paths is active at any given time whether or not a particular signal input path is selected for output. Thus, in an exemplary 128:1 multiplexer, each of the 128 input paths remains active at all times. In an exemplary high speed 128:1 multiplexer, where source coupled field effect transistor logic is employed in order to increase switching speeds, maintaining each of the 128 input paths in the active state implies that each of the transistors used in the 128:1 multiplexer is biased in the active or saturation modes at all times. In this type of a multiplexer, keeping all of the unused signal paths active represents a significant waste of power since only one signal path is used at any given time. When the multiplexer is employed in a communications node such as an orbiting satellite, where available power must be derived from solar energy and batteries, the use of equipment which consumes significant power causes an increase in payload weight, required cooling, overall deployment cost, and complexity of the communications system. These costs must, in turn, be eventually passed on the subscriber of the satellite communications service.
Therefore, what is highly desirable, is a high speed multiplexer which does not require inactive signal paths to be in an active state. What is also highly desirable, is a high speed multiplexer which does not require complex decoding logic in order to select the signal path through the multiplexer stages.